MOS bootstrap inverters and MOS push-pull drivers are well known in the art. They are frequently combined in an integrated circuit to produce circuits which are capable of driving large capacitive loads with fast rise time waveforms. However, such circuits provide output voltages which are either equal to the power supply voltage level or the ground voltage level, and are consequently not suitable for providing a regulated bias voltage which tracks with the threshold voltage of the MOSFETs. Other bias circuits have been implemented utilizing MOSFETs, but most of them are DC circuits. Prior circuits which are capable of providing a switchable bias voltage have very poor transient response, that is, they do not have rapid rise and fall times. Known MOS circuits are not capable of providing an output pulse having sharp rise and fall times and yet having a pulse magnitude which tracks with the MOSFET threshold voltage.